This is a good point you've made before. I think the big thing is many people can't wrap their head around boost control. It can be tricky to have good boost control with a 3" mid pipe - doable, but it can require putting some work in.

Of course I've aged out of stinky loud exhausts .

Dale

 

Yep, boost control is everything on stock ecu. I also hate stinky and even worse loud exhausts in my older age. Lol

 

Supra pump straight drop in can handle more power than the twins can make. Denso quality. 12psi watching afr. ....... could be ok with the base map in the pfc or have Ari mod it a bit from RX7.com. I am pretty sure 12psi should work if injector duty is under control. Watch to cool nights

I would avoid the midpipe unless you are 100% sure you have no creep. You will BLOW YOUR MOTOR. I would save midpipe for bigger injectors and tune. Or if you must try mid pipe use a restriction plate or something.

 

That's a pretty badass engine you built him.

 

remove the factory restrictor pill and by pass or eco from and wastegate solenoids? Can you please elaborate or point me in this direction?

thank you

 

The fuel cut table I have shows that they will hit fuel cut on the stock ecu at 12psi in the top of the rev range.

I would hate to have a car where I have to "Watch cool nights". Also... How can they watch anything with a stock ECU?

While dual Hallman MBC's do technically work as a replacement for the stock boost control solenoids, they suck for boost response and transition. You lose some pre-spool of the secondary and you lose the ability of the ECU to hold open the precontrol gate after transition, which creates an unwanted restriction on your secondary turbo. It is not ideal. Power FC allows you to retain computer control of the WG and PC solenoids and control boost. Win-win. I have used both methods to control the twins.

 

[QUOTE=alexdimen;12446231]The fuel cut table I have shows that they will hit fuel cut on the stock ecu at 12psi in the top of the rev range.

I would hate to have a car where I have to "Watch cool nights". Also... How can they watch anything with a stock ECU?

You watch with a stock ecu, haltech, pfc, or any ecu..... with an afr gauge. I wouldn't want to be running boost at a level were I have to "watch cool nights" either. Unfortunate some people apparently set themselves up that way and if they do not have enough restriction they can creep.... creep can equal blown motor...
That is why I said I would 100% make sure you have no creep. If you must have a midpipe and you have no creep, "watch the cool nights". Watch your afr.
There was a big discussion a long time ago that 10psi does not = 10psi for afr. Like exhaust gas left in chamber for another cycle is not going to equal a fresh stroke. Etc, etc. OP can do whatever he wants. I would simply advise against a midpipe because in my own experience I had issues. I know a few people whom had issues.
Supra pump will help after pfc (or whatever) and you want to raise boost up to around 12. I should have clarifed that it may not or would not help on stock ecu.... does that sound better?

 

I have dual "Home-Depot", i.e., homemade, ceramic ball and SS spring boost controllers w/o the pills in the lines. The primary is set at 11 psi, and the secondary at 10 psi. I really like the response and transition. At the normal transition point, the secondary turbo comes in with a satisfying kick and no noticeable dip in power in between.

My setup:
https://www.rx7club.com/3rd-generati...ht=ball-spring

 

I'm not saying it doesn't work. I am saying it doesn't work as well as the stock system.

FD's with MBCs are still a blast to drive. I had one, but eventually I wanted to compete with and beat modern cars at autocross and the stock control turbo system is much better suited for that.

I've been back to back to back from stock ECU boost control (was hitting fuel cut), so I went to MBCs, and then to PFC with stock solenoids.

The "kick" at transition I would guess is from the secondary turbo not being spooled up properly by the PC duty cycling. With a MBC the precontrol is closed until the spring pressure is overcome and it is suddenly slammed with boost pressure. It's like an on-off switch. The stock system and PFC duty cycle the PC, which allows more exhaust flow through the secondary turbine to spin it up during primary boost. If the secondary is not pre-spooled you are opening the turbo control actuator door and slamming a slow turbine with exhaust flow.

With an MBC at the top end after transition there is going to be a restriction at the secondary turbo because you can't isolate and force the precontrol door wide open like the stock ECU or PFC does.

With MBC's how can you ever be sure if you're controlling boost with the PC, WG, or some combination of the two. There's many good reasons Mazda separated them and controlled them individually.

 

That all may be true, but I just wanted a relatively simple way to limit boost to safe levels w/o excessively limiting performance with my enhanced intake, IC, DP, and catback. My FD is just an enjoyable toy for the weekends, etc., since I have a real racecar for the track. I'm guessing I added close to 50 HP with these mods, and that's plenty for me on the street. My Autometer boost gauge will record any overboosts, and I haven't seen any in the 15 years I've had this setup installed.

 

Glad we’ve been having this discussion. Bone stock JDM 94 (so no pre-cat...you could consider that a “mod” compared to US.) Installed the Autoexe intake, got worried about over boost, and installed a gauge.
In 1st I saw 15psi before I backed of. In 3rd/4th I saw 12/10/12.

 

I disagree that FD with MBC on precontrol and WG actuators doesnt work as well as stock.

When I had my FD on stock ECU, 10psi boost with just upraded smic (stock duct type), downpipe and catback I had the boost and transition dialed in with Hallman Pro RXs so it was seamless (and it stayed dialed in- didnt wander with weather, elevation, time, etc).

I had raced the previous season in stock class (just catback) and hated the stock sequential transition with the dip and spike.

Now with ROM tuned ECU, 14psi downpipe, midpipe, catback, huge SMIC and M2 airbox the transition IS a bit wonky on the MBCs. Primary hits hard, runs out of flow so boost drops before transition and then bam 2nd turbo comes on full boost. Cant fix it.

 

Just to clarify - I am not saying you won't be able to control boost with MBCs. I had MBCs and found that boost control amount was actually more consistent than the stock system. That would make sense because you are working against spring pre-tension in the MBC and it always cracks open at the same pressures. The stock system is bleeding pressure based on a set point and target, which will react differently depending on air density and it's effects.

What I am saying is there are secondary functions to the pre-control door that you lose direct control of when you have MBC's.

You can't be sure that all of these things are happening:
1. Only the pre-control door is opening prior to transition so your secondary is getting pre-spooled as much as possible
2. Your pre-control door is completely open post transition
3. Your boost level is at your target(s) across the rev range
4. Transition is just right (how did you even tune transition with MBCs? that is controlled by the TCA)

With MBC's you have too much to balance, which is why controlling the function of each actuator via ECU is the only way to go.

Example:
Dave's pre-transition boost level is 11 PSI. How is that being regulated? If ONLY the PC is regulating primary boost at 11 psi, then he is getting good pre-spool of his secondary turbo. BUT that isn't possible because that would mean the WG is opening at 10 PSI intake pressure so the WG is opening before the PC. You might have a shot at getting it to work if your PC is set lower than your WG. And then either your primary boost is lower or your secondary boost is flirting with fuel cut on the stock ECU.

 

Make sure that your boost gauge is accurate. I say this because I had one that was two lbs off. Mine was the other way it read 10 psi when I was really at 8.

 

Alex, I don't pretend to know everything about boost control with MBC's or other methods, but I can tell you for a fact that I do get 11 psi on my boost gauge before transition, and I get 10 psi after with very little drop in between. I set those levels so that I would get a little more torque on the primary, and also be limited to 10 after transition so that there would be no chance of triggering fuel cut.

You obviously have done much more sophisticated studying on the subject, so I will not argue the point that there would be a setup that works better. All I have to say is that I think my setup works very nicely and I have no reason to want to do anything different.

 

I totally believe you and if I'm coming across combative/doubtful/negative it isn't my intention. I just want everyone to have as much fun with their 7's as possible and I'm sure you are.

I also want to gain a better understanding of how these things work so I put this kind of stuff out there to be challenged and to challenge others.

 

This is becoming a boost control thread .

Don't forget electronic boost controllers. I have an AVC-R and have had it for ages, works perfectly with smooth power all the way up.

Unless you have a way to control the factory boost solenoids (PFC) you need to remove them from the equation. Trying to play with pill size or use an MBC with them is super difficult.

The AVC-R is an unsung hero - it's complicated since it has so much functionality but that joker works. Boost by RPM, boost by gear, self-learning capability, even has an input to lower or raise boost - I have mine tied to my water injection, if the water tank is dry is basically turns boost control off. Also you can pick between 2 maps or disable the boost controller.

Dale

 

How do you have it plumbed if it is controlling pre control also? Did you connect the actuators in parallel? I guess you could change the oem spring rates to ensure it favours the pre-control actuator to ensure peak performance from your set up if running the actuators connected in parallel.

I've drilled out my pills on my current build and will be running a pair of quality manual controllers. I've got a little more head room as being an S8 my boost on the OEM ECU is 10.8 PSI so I'll be setting my primary boost to 10.5 and secondary to 11 to ensure my pre-control gate is open fully during secondary operation... Or I may alter the springs and run 11 on both.

Interesting thread! I love how these cars are 30 years old and still confusing people, got to love the set up with the twins .

 

I have my AVC-R set up with the waste gate and precontrol both T'd into the AVC-R actuator. Lots of people get worked up about this, "it's not gonna work!" "your turbo won't spool right!" - nope, it works perfectly.

I did that and also lowered the switchover point in the PFC. I have 2 settings, .8 (12psi) and 1.0 (14.7psi). Both are rock solid, hit hard with boost on the low end, and I have ZERO transition, just steady boost all the way up. I do have 99 280hp turbos with a ported waste gate.

People that have driven my car have commented on how much low end grunt it has. The combo really works well. There's no "RPM's drop down, have to spool back up" or anything weird, just floor it and get the boost you want, any time you want.

Dale

 

With the Hallman pro-rx on wastegate and pre-control you leave the stock ECU controlling TCA.

The perfectly smooth transition is achieved by 1st leaving precontrol MBC low and using the WG MBC to adjust post transition boost levels (you cant do this properly if you have boost creep). This eliminates variable of precontrol exhaust bleed affecting boost levels as when on primary turbo operation.

Then you tighten the Pre-control MBC till torque is stable on the transition to 2ndary turbo (boost gauge will flicker down- but no drop in torque because engine VE just jumped up).
Once you get Pre-control MBC dialed primary boost matches 2ndary because Mazda sized things to work this way.

It takes a bit of back and forth, but ends up working beautifully in my experience.

I bought my FD with dual MBC and went back to stock turbo control and pre-cat for Stock class racing. Hated the kick of torque when 2nd turbo came on with Stock class car (cat back exhaust). Went back to ASP with MBCs and downpipe and was able to dial in the transition perfect again in a couple hours. Was surprised it stayed perfect for 4 years till I modded up to 14psi.

 

I will say with the manual boost controllers the good ones do work great but you start getting in the pricing territory of a used EBC really fast. Especially since you would need 2. But you would also need a place to mount the EBC in the car cleanly.

Blue TII, that's awesome that it worked that well for you and Thanks for the how-to on the tuning, that's the step that gets missed a lot in these discussions!

Dale

 

This is kind of the setup I've been thinking about with my car. Currently it has a 3" downpipe, a Rx7Store high-flo cat, and stock cat-back. The intake side is completely stock as well. I want to pick up a cat-back (mostly because the car is too damn quiet, and there's a hole in the muffler), but I'm worried about the stock ECU and having boost issues. Wondering if I should get a restrictor plate as well to help keep things in check, or just by pass the cat-back and do the PFC first...

 

Make sure you have a boost gauge. As stated, if you can keep boost to 10psi you will be good, either with boost control or a restrictor plate.

Dale

 

I do have a gauge, but gotcha. I guess I could pull out the restrictor pills to be super safe, but I might just go with the PFC first and save myself some potential stress.

 

For what it is worth, I didn't have any boost creep using the stock intake with the HKS downpipe, bonez high flo cat, and racing beats cat back, but I was using the PFC on a base map tune.

If you have a boost gauge I'd just take it out for a drive once you get everything installed and see what it tries to do.